Modulation system



Oct. 11, 1932. c, CULVER 1,882,122

MODULATION SYSTEM Filed Aug. 3, 1928 INVENTOR.

zay'ig s/f. 614 M22;-

ATTORNEY.

, Patented Oct. 11, 1932 UNITED STATES.

PATENT; oFFlcE CHARLES CULVEB, OF NOBTHI'IELID, MINNESOTA, ASSIGNOIB. TOWIRED BL'DIO, INC 01 NEW YORK, N. Y., A CORPORATION OF DELAWARE nonunionsys'rnu Application filed August 8, 1828. Serial No. 297,200.

a My invention relates to modulating systems in general and morespecifically to systems for modulating the energy of continuous wavetransmitters.

LU An object of my invention is to provide an improved modulating systemfor continuous wave transmitters.

Another object of my invention is to provide an improved modulatingsystem for 1 radio telephone and broadcast transmitters whereby aminimum of distortion is produced.

Still another object of my invention is to provide an improved systemfor modulating the energy of continuous wave high frequency transmittersemploying electrically blaianced circuit arrangements of thermionic tes.

Abetter understanding can be had of the modulation system of myinvention by referring to the specification following and to theaccompanying drawing wherein is illustrated the modulation system of myinvention.

A diagrammatic circuit arrangement is shown employing in combinationahigh frequency electrical generating circuit, a balanced amplifiercircuit, a modulation circuit, and a load circuit which might be a spaceradio radiating system as illustrated, a wired radio system, oradditional amplifier circuits.

The high frequencygenerator includes thermionic tube 1, having controlelectrode '2, cathode 3 and anode 4. Control electrode or grid circuit 5includes mechanically vibratile element 7 which may be any means forsustaining oscillations of constant frequency, such as a. quartz crystalhaving piezo electric properties. Radio frequency choke coil 9 excludesradio frequency energy from source' V of grid biasing potential 10. Theanode or plate circuit 6 of thermionic tube 1 includes radio frequencyinductance-capacity circuit 8 and source of anode potential 12. Circuit8 is coupled to input circuits 13 and 18 of thermionic tubes 14 and 28respectively. Electrodes 2, 3 and 4 of thermionic tubes 14 and 28correspond to electrodes 2, 3 and 4 of thermionic tube 1. Thermionictubes 14 and 28 have a common output circuit15, the

energy from which is transferred to load circuit 20. Load circuit 20 maybe a wired.

radio system, additional amplifiers, ,or as illustrated, a space radioradiating system. Anode potential for thermionic tubes 14 and 28 issupplied from source 22. Capacity 16 completes the radio frequencyoutput circuit. The anode potential of thermionic tubes 14: and 28 isgoverned by the resistance of thermionic tube 23. The anode-cathodevresistance of thermionic tube 23 is in series with source of potential22 and anodes 4 of thermionic tubes 14 and 28. Electrodes 2, 3 and 4 ofthermionic tube 23 correspond to electrodes 2, 3 and 4 of thermionictube 14. Radio frequency choke coil 17 excludes radio frequency energyfrom thermionic tube 23. A source of current variations is produced byvariable resistor 27 and source of potential 26. Variations ofelectrical energy are transferred to control electrode-cathode circuit24 by transformer 25. Source of potential 29 provides the properoperation of thermionictube 23 by selecting the pro er part of thecharacteristic curve. Varia le resistor 27 is herein illustrated as anordinary v telephone microphone.

It is obvious that any source of variable electrical energy may beemployed, for example a light-sensitive cell of selenium.

Variations of potential add to-or subtract from the normal operationalpotential of control electrode 2. Variations of potential suppliedcontrol electrode-cathode circuit 24 produce corresponding changes inthe anode-cathode resistance of thermionic tube 23. As the resistance ofthermionic tube 23 is varied or modulated, the potential supplied anodes4 of thermionic tubes 14 and 28 will be likewise varied or modulated.

It is obvious that the modulation system of my invention may be employedin systemswherein only high frequency generators are employed. In sucharrangements the modulation system of my invention may be employed in asimilar arrangement to t at illustrated in the accompanying drawingwherein the system is applied to thermionic tube amplifier systems. As aresult of this arrangement, the power output of the high fresupply tosaid first mentioned thermionic m strict accordance with thevoice-generated t be potential impressed upon the modulator tube anddistortion of the audio frequency is there- 5- by revented.

' Y T e modulation system of my invention has other advanta es. In theconstant current system of mod ulation power voltages developed acrossthe inductance forming the choke,

are in mag -instances excessively hi h, with the result t at theoscillator or ampl' er tubes are compelled to carry a load whose valueis many times the non-signaling-value. As an example suppose that theoscillator or aml5 plifier tubes are overloaded four times thenon-signaling value and an avera e of three halves the non-sigre salingvalue.- nless ex-' cessively large'tu are used, the tubes are overloadedand consequently a material 80 shortening of their life results. In themodu" lation system of my invention, theabsence of the largechokeinductance prevents distortion. It is a well known fact that the voltagedeveloped at the terminals of the choke in the constant current'systemwill be a function of the frequencies impressed upon theinductance. The result follows that the wave form will be distorted, andhence the wave a replica of the voltage curve impressed upon the grid ofthe modulator tube. In the modulation system of m invention the power iscontrolled or modu ated by what amounts to an ohmicresistance. Thedistortion, which results from employing inductance, isthereforeavoided. Batteries are illustrated in the accompanying drawingv andreferred .to in the foregoing specification. It is obvious that ployed.It should be understood that my invention may be employed in circuitsother than the oneshown in the accompanying drawing. v

It is to be further understood that a crystal controlled driver circuitnot essentialibut that any master oscillator or source of high frequencyenergy may be employed. I realize that many modifications of themodulation to be understood that my invention is not restricted to theaccompanyin drawing or to the foregoing specification int only asdefined in the appended claims.

I claim:

- of thermionic tubes having cathode, control electrode and anodeelectrodes, said thermi onic tubes connected. in an electrically bal- 00anced circuit arrangement, common potential ed in series with the commonanode potential form of the voltage curve impressedf'upon. theoscillator or power amplifier will not be any suitable source of energymay be em-' system of my invention are possible and it is 1. In amodulation system the combination 1 2. A modulation system comprising incombination electrically balanced circuit arrangements of thermionictubes and a thermlonic tube connected in series with a common source ofenergy supplied to the anodes of said first mentioned thermionic ,tubeswhereby theresistance of said last mentioned thermionic tube controlsthe ener supplied said first mentioned thermionic tfibes. 3. Amodulation system comprising in combination electrically balancedcircuit arrangements ofthermionic tubes employed as amplifiers and athermionic tube having its cathode-anode resistance connected in serieswith a common source of electrical energy supplied to the anodes of saidbalanced thermionic tube amplifiers.

4. A system for modulating hi h frequency, energy comprising in comination thermionic tubes connected in a balanced amplifier arrangement,said thermionic tubes having common anode circuits, a common source ofanode potential for said anode circuits, and the anode-cathoderesistance of another thermionic tube connected in series with the anodesupply potential of said first mentioned thermionic tubes.

5. A broadcasting system comprising in 95 combination a source of highfrequency signaling ener thermionic tubes connected in an electricallybalanced circuit arrangement, said thermionic tubes having a commonsource of anode potential, athermionic tube the resistance of which iselectrically connected in series with said source of anode potentialand-means for varying the resistance of said last mentioned thermionictube thereby varying thepotential supplied said anodes;

6. A system for modulating high frequency signaling energy-according tolow frequency variations comprising in combination electrically balancedthermionic tube generators having a common source of anode potential, athermionic'tube the resistance 'with said source of anode potential andmeans for causing the resistance of said last '115 mentioned thermionictube to vary according to variations of current impressed there 7. Amodulation system comprising in combination a source of high frequencysignaling energy, a plurality; of thermionic tubes employed inelectrically balanced amplifier circuit arrangements, said thermionictubes having a-common' source of anodepotential, athermionic tube theanode-cathode resistance thereof connected in series with said. sourceof anode potential, and means for varying the resistance of said lastmentioned thermionic tube according to fi equencies of a lower orderthan said high frequency.

8. A radio signaling system comprising means for radiating oscillations,an electron 5 tube oscillation generator associated with said radiatingmeans, a push-pull electron tube amplifier interposed between saidradiating means and said oscillation generator, a source of anodepotential for said amplim fier, and means including an electron tube theinternal resistance of which is in series with said source of anodepotential for varying the anode excitation applied to said amplifier inaccordance with a desired modula- 15 tion of signaling waves.

In testimony whereof I aflix m si nature.

CHARLES A. UL R.

